There are known whole body MRI systems (super-conductive, permanent magnets and resistive magnets), having field homogeneity in the air gap, i.e. imaging volume, in the center of the magnet and, therefore, any part of the body has to be placed in the center of the magnet to be imaged.
However, the whole body magnets are generally very expensive to purchase and maintain and, therefore, they are not widely available for the substantial need to provide a regular and frequent imaging like mammography as well as imaging of other organs. Prior art electro-magnets such as described by Watson et al and Miller et al. and other prior art iron core magnets have a substantial edge fringe field effect, which makes it hard to image beginning immediately at the magnet edge or even proximal to the edge of the magnet due to lack of sufficient field homogeneity. In addition, those types of the prior art magnets, of the iron core electro- or permanent type, typically have a structural design to provide a high strength magnetic field at a large central air gap.
In U.S. Pat. No. 5,049,848 a magnet configuration for MRI mammography is disclosed. The magnetic structure 50 has a rectangular shaped magnet with at least two parallel magnetic sources 5,6 connected by a ferromagnetic core flux path defining an air gap for imaging. A remote shimming C-shaped magnetic source is preferably used to decrease the front edge fringe effect of the magnetic structure 50 to create a relatively homogeneous field in the air gap beginning at the front edge for effective imaging.
However, a relatively small and economical MRI device for mammography is still being sought. Thus, additional magnet configurations capable of providing field homogeneity at the front edge of the magnet are desired.